The present invention relates to a touchscreen apparatus for providing input to a computer and in particular to a system for providing feedback to a touchscreen operator indicative of touchscreen input accepted by the computer.
A touchscreen typically comprises a set of photodetectors and a set of light emitting diodes (LEDs), one LED corresponding to each photodetector. The photodetectors and LEDs are distributed along the edges of a computer terminal screen with each LED and its corresponding photodetector being mounted on opposite edges of the screen so that each LED transmits a beam of light across the screen to its corresponding photodetector. The LEDs and photodetectors are usually arranged so that some light beams produced by the LEDs traverse the screen in a vertical direction while other light beams traverse the screen in a horizontal direction, and the horizontal and vertical light beams are spaced so as to form a regular, rectangular grid in front of the screen. Parallel beams are close enough together so that when an operator touches the screen with a finger, the finger usually prevents at least one vertical beam and at least one horizontal beam from striking its corresponding photodectector. Each photodetector produces an output signal of a high or low logic state depending on whether or not it detects the corresponding light beam, and the position of the operator's finger on the screen can be ascertained from the states of the photodetector output signals, provided the finger intercepts at least one horizontal and one vertical beam. The computer is normally programmed to determine from the horizontal and vertical beam intercepted that the operator has touched a point within a particular "touch zone", a rectangular area surrounding the intersection of the beams.
The computer may be programmed to respond to the touching of a particular touch zone similar to the way that it might otherwise be programmed to respond to the operation of a pushbutton. Thus, touchscreens are commonly used in computerized systems such as digital oscilloscopes which display menus, "selectable" icons or other objects on a screen because a touchscreen permits an operator to select an object or menu item by touching its image on the screen rather than, for example, by depressing a pushbutton corresponding to the selectable item. In such an application, a touchscreen not only eliminates or reduces the need for pushbuttons, it also tends to reduce opportunity for operator error since item selection is direct and intuitive.
Despite the many advantages of touchscreen input systems, they do have some drawbacks as opposed to keyboard or pushbutton-input systems. Because pushbuttons can be seen and are visually distinct from one another, when an operator depresses a particular pushbutton providing input to a computer, the operator can be reasonably certain that computer will recognize that particular pushbutton as having been depressed and not some other pushbutton. However, since an operator normally cannot see the light beams in a touchscreen, touch zones may not be visually distinct from one another. Thus the operator may not be certain that the computer has recognized that the operator has touched a particular touch zone and not an adjacent touch zone, particularly when light beam spacing is fairly close. In addition, since an operator's hand shakes somewhat, the edge of an operator's finger may intermittently intercept light beams causing the computer to think that one or more touch zones are being repeatedly touched and untouched, and the operator may have no indication of this.
What is needed is a system for providing feedback to an operator indicating the computer's perception of touchscreen operations.